Sharks have been around for a long time -- we're talking a few hundred million years. They predate humans and even dinosaurs. Sharks have survived everything Mother Nature has thrown at them over that span, so you'd think they'd be around for another couple hundred million years. Sadly, this may not be the case. The reason? Man. Specifically, the overfishing of the species by commercial and recreational fishermen.

Research indicates that about 100 million sharks are killed each year by humans -- roughly 11,000 sharks every hour, around the clock [source: HSUS]. These numbers may even be on the low side, since the estimate is based only on the reported catch numbers. It's likely that many sharks are caught without being reported.

Commercial fishing accounts for a large part of the overall number of sharks caught. Sometimes the shark is the target, but many times it's just a victim of something called bycatch. This is when a commercial boat hauls in other types of fish in addition to the species the fishermen are after. Bycatch is a common result of longline fishing, when workers on the boats spool out hundreds of feet of fishing line with up to 2,000 baited hooks spread along its length. Tuna and mackerel are fished using the longline technique, and the resulting shark bycatch has had a drastic effect on the overall population. The sharks that are caught as bycatch are often killed or injured in the process and usually thrown overboard.

There are other species of fish that are more heavily targeted than sharks, but they don't face the same threat of endangerment. One reason is because sharks typically reproduce only once a year, and they carry just 10 to 40 pups per pregnancy. This sets them apart from many other fish that deposit thousands of eggs at a time. The overfishing combined with the long gestation period and limited amount of young they produce has placed several species of shark on the protected list.

While commercial fishing has put a dent in the shark population, recreational fishing has done its fair share to endanger sharks as well. We'll take a look at the impact of recreational fishing on the next page.